I. The Aspergillus toxin alpha-sarcin produces a precise cut near the 3'-end of 28S ribosomal RNA in vitro only if the ribosomes are pretreated with puromycin and EDTA. Alpha-sarcin can also behave as a general nuclease in vitro under appropriate conditions. In order to investigate alpha-sarcin's in vivo activity, we injected it into living Xenopus oocytes and analyzed the resulting RNA. We have also investigated whether ricin, Shiga toxin, and Shiga-like toxin variant (SLT-IIv)produce similar effects in oocytes. II. During early development Xenopus replicates its DNA nearly as fast as E. Coli in log phase; perhaps indicating that oocytes may be an excellent source of DNA repair activity. We have investigated pyrimidine dimer repair by microinjecting uv- irradiated DNA into oocytes and assaying for repair using 2 methods: (1) Transformation of repair deficient E. coli mutants with the microinjected DNA; (2) Absence of pyrimidine dimers using UV-Endonuclease and denaturing agarose gels.